Digitimer
DS2A-Mk.II & DS3 Isolated Stimulators
Brief pulses of electricity are used in various biomedical research applications as a stimulus to excite nerve or
muscle fibres. Several factors need to be considered when choosing the right stimulator.
In order to minimise artefacts introduced into electrophysiological data, it is desirable that the
stimulator should be electrically isolated both from ground and from the trigger device.
The voltage required to send current through tissues can vary greatly, making it important to have
control over the stimulus driving force.
Large impedance variations during an experiment can result in loss of the stimulus. In this event, a
constant current stimulator may be more suitable.
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Our two isolated stimulators either provide constant voltage (DS2A-Mk.II) or constant current (DS3), giving you
the ability to choose the stimulator which best suits your experimental needs.
DS2A-Mk.II Constant Voltage Stimulator
The latest version of the DS2A gives:
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External control of pulse duration.
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Overload protection circuit preventing
current in excess of 50mA being delivered
DS3 Constant Current Stimulator
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Four current ranges allow precise control of
output between 2µA and 32mA.
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Output discharge (Clamp) circuit prevents
capacitance build-up during stimulus trains,
which is important to prevent stimulus loss.
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90V compliance provided.
Both units feature:
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Accurate and reproducible stimulus characteristics.
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Switchable polarity, variable output and duration ranges (20µs to 2s).
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External pulse duration control through the BNC trigger input.
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A single-shot button, which operates irrespective of trigger inputs.
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Cases manufactured from insulating material may be rack mounted using an optional mounting frame
(Model D121-11) available from Digitimer Ltd.
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Power provided by standard batteries. Note that current is only drawn during pulse delivery.
Technical Specifications
Output:
DS2A-Mk.II (Constant voltage)
Two ranges provide 99V (high) and 9V (low) maximum output. A multi-turn dial
allows output to be selected as a percentage of maximum. Square wave pulse
profile with typical rise time <1µs and fall time <3µs into resistive load.
DS3 (Constant current)
Output between 2µA and 32mA. Control is achieved by a variable range switch
with four selections (10µA, 100µA, 1mA, 10mA) and a three-turn dial.
Pulses from high impedance stimulators (constant current units) can result in
cells “charging-up” between stimuli, leading to stimulus loss. This problem has
been overcome in the DS3, which has an Output Discharge (Clamp) Circuit
that operates for 20µs after each stimulus pulse. This will discharge cells with
capacitances as high as 1000pF.
Pulse Duration:
Range: 20µs to 2s. One dial allows continuous adjustment from 2 to 20, while
another is used to select the range (from 10µs, 100µs, 1ms, 10ms, 100ms
or external source). Internal pulse duration values have ± 10% accuracy.
Output terminals:
A pair of 2mm touch-proof sockets on the front panel spaced at 0.75”.
Polarity Switch:
Normal: Red output terminal positive.
Reverse: Red output terminal negative.
Indicator:
An LED operates for the duration of each output pulse.
Compliance:
(DS3 only)
90V from 10 x 9V batteries. This reduces to 87V at the top of each output
range. Note that battery voltage will drop from 9V to ~6V with “old” batteries.
Overload:
(DS2A only)
An automatic overload circuit prevents excessive output current being drawn
by reducing the output pulse duration to <10µs when a current of greater than
50mA is detected.
Single Shot:
A single-shot push button is provided. This operates at all times irrespective
of trigger input.
Trigger:
A positive pulse of between 3V and 20V is required to trigger the stimulator.
The trigger input current varies from 6mA to 62mA over the above voltage
range. Trigger pulse duration should not normally be less than 4µs.
Trigger Isolation:
Optical coupling is employed between the trigger source and the stimulator
circuitry. The capacity coupling is less than 3pF.
Batteries:
11 x PP3, IEC-6R61 style batteries. Current is only drawn when delivering a
pulse. Note that battery test sockets are built-in.
Mounting:
One or two stimulators may be mounted in a 19” rack using a specially
fabricated frame (model D121-11) available from Digitimer Ltd.
Dimensions:
Panel size: 190mm x 110mm. Depth: 80mm over knobs.
Weight:
800g complete with batteries.
Digitimer reserve the right to alter specifications and price without prior notification
Digitimer Ltd, 37 Hydeway, Welwyn Garden City, Hertfordshire, AL7 3BE, England
Tel. +44 (0)1707 328347; Fax: +44 (0)1707 373153;
E-mail: sales@digitimer.com; Website: www.digitimer.com